1. FIELD OF THE INVENTION
This invention relates to displacement sensors and, more particularly, to a displacement sensor, which measures linear displacements, angular displacements, etc. optically with a semiconductor laser as a source of light.
2. DESCRIPTION OF THE RELATED ART
In the prior art, there have been displacement sensors for optically measuring linear displacements. One such displacement sensor comprises a housing, a spindle provided therein for displacement in the axial direction, a probe provided at one end of the spindle, and a scale provided at the other end thereof and having an optical lattice extendinc in the direction of displacement. The housing furtheI accommodates a light source for projecting light onto the scale and a photoelectric transducer for converting light from the scale to an electric signal.
In the above displacement sensor, if the scale is subject to thermal expansion and contraction with ambient temperature changes, it will cause variations of the clearance between the scale and photoelectric transducer or cause generation of thermal stress in the scale. In this case, high accuracy measurement can not be obtained.
In the meantime, in the photoelectric displacement detection, it is desirable that the optical signal has high contrast between the brightness and darkness. To attain this, it is desirable to use a semiconductor laser as a source of light. The semiconductor laser, however, generates great heat. Therefore, the scale which is disposed near a semiconductor laser is subject to thermal expansion, thus leading tc errors in the displacement detection and making it impossible to obtain high accuracy measurement.
An object of the invention is to a displacement sensor, which can solve the above problems and permits a great heat generation semiconductor laser to be used as a light source with less thermal effects thereof on the accuracy of measurement.